1. Field of the Invention
The present invention relates to a lithium secondary battery and to electrodes for a lithium secondary battery.
2. Description of the Related Art
As a result of miniaturization of electronic instruments, there has been an increasing demand, in a battery used as an electric source, for the development of secondary battery which is small in size, light in weight and high in energy density and is also able to be charged and discharged repeatedly.
With regard to a secondary battery meeting such a demand, a secondary battery using a nonaqueous electrolyte has been practically used and such a battery has several times higher energy density as compared with the conventional battery using an aqueous electrolyte. An example is a nonaqueous electrolyte secondary battery in which a lithium-cobalt composite oxide, a lithium-nickel composite oxide or a lithium-manganese composite oxide is used for a positive electrode and an alloy or a carbon material is used for a negative electrode.
Since a combustible organic solvent is used as an electrolyte in the above nonaqueous electrolyte secondary battery, there is a problem that, in the case of overcharge or the like, a thermally unstable state is resulted and properties of the battery are deteriorated due to side reactions other than the battery reaction and, in addition, there is a possibility that safety of the battery is greatly spoiled due to burning of the organic solvent.    Patent Document 1: Gazette of Japanese Patent Laid-Open No. 2007/005,267    Patent Document 2: Gazette of Japanese Patent Laid-Open No. 2004/296,108